Acute exposure to inorganic arsenic compounds can lead to fever, cardiac arrhythmia, cardiac failure, hepatomegaly, melanosis, peripheral neuropathy, hematopoietic effects, loss of peripheral nervous system function, leukopenia, anemia, or death. Chronic exposure can lead to neurotoxicity, demyelination, liver injury, peripheral vascular disease, and carcinogenesis resulting in hemangiosarcoma of liver, skin cancer, and lung cancer. The majority of occupational exposure to arsenic is in the manufacture of pesticides, herbicides, and other agricultural products, and in the smelting industry. Exposure to arsenic also can result from environmental exposure to contaminated ground water. Metabolism of arsenic is complex as arsenic can be trivalent or pentavalent and can form many different compounds. Methylated and dimethylated arsenic compounds are the major transformation products in vivo and are rapidly excreted in urine. While methylation typically is regarded as a mechanism for detoxification, certain methylated arsenic compounds that contain AsIII are more cytotoxic and genotoxic than arsenate (the most stable form of arsenic) and arsenite (AsO33−), and also more potent inhibitors of GSH reductase, thioredoxin reductase, and pyruvate dehydrogenase than arsenite. See, Lin et al., J. Biol. Chem. 277(13):10795-10803 (2002). ASMT (also referred to as AMT) is an enzyme that methylates arsenite using S-adenosyl-L-methionine as the methyl group donor. ASMT is expressed in the liver, kidney, and brain in humans. In rats, ASMT is expressed in heart, adrenal glands, urinary bladder, brain, kidney, lung, and liver.